The present invention relates to a rolling apparatus having low heat conductivity, in particular to such a rolling apparatus to be used to systems transporting within furnaces at high temperatures such as ceramic kiln cars, conveyors for continuously heating treatment or paint baking trolleys, otherwise to usage under conditions where heat is conducted to the rolling apparatus via a housing or a shaft from a heat source outside of the rolling apparatus as an iron-steel equipment, resulting to have high temperatures (hereafter called as xe2x80x9cthe rolling apparatus used in the vicinity of the heat sourcexe2x80x9d).
The invention also relates to a rolling bearing for supporting a main shaft of a motor of air blowing fan used as a cooling fan of micro processor (IC, MPU) to be incorporated into air conditioning fans, ventilating fans, personal computers or servers (hereafter called as xe2x80x9cthe rolling bearing for fan motorxe2x80x9d).
Further, the invention relates to a rolling bearing to be suitably used to copiers (PPC: white-black, color, analog, digital or other kinds), laser beam printer (LBP), facsimile (FAX), or office machinery such as compound machines of them (hereafter called as xe2x80x9cthe rolling bearing for office machineryxe2x80x9d).
In the rolling bearing, members as a movable member, a supporter and rolling elements are composed with metallic members as steel. At the interior of the rolling bearing, a lubricant as a grease is circulated or charged for effecting lubrication. Such rolling bearings are used without any problems under ordinarily using conditions.
On the other hand, in the systems transporting within furnaces at high temperatures such as ceramic kiln cars, conveyors for continuously heating treatment or paint baking trolleys, as the inside of the furnace is at high temperature, the heat is conducted mainly from the housing, that is, from the outer ring into the inside of the rolling bearing to heighten temperatures thereof. The inner ring, outer ring, and rolling elements are mainly composed with a steel for bearing (SUJ2).
As motors of cooling fans of micro processors to be incorporated in personal computers or servers are demanded to be small sized or quiet, a so-called brushless DC motor is employed, where a rotor is furnished with a permanent magnet and an electromagnetic field is formed by the core and coil of a stator to rotate the rotor. In motors for air blowing of a middle sized type, AC motor by an inverter control is used, and also similarly to the above, the electromagnetic field is formed at the stator side to rotate the rotor.
Such rolling bearings for fan motor are structured with a duplex bearing effected with a normal position or constant loadxe2x80x94pre load for securing rigidity of a main shaft. In the rolling bearing, a bearing ring and rolling elements are composed with a bearing steel or heat resistant steel, and a holder is a metal-made press holder, and in particular, for the small sized bearing, resin-made crown holder is used. In these bearing units, depending on attachment of the rotor, there are cases of the outer ring rotating and the inner ring rotating.
The office machinery such as copiers, LBP, FAX or these compound machines has been demanded to have more advanced high performance (heightening the treating speed per sheet of paper) and to be more compact. The office machinery has always been demanded to be improved as such. For satisfying these requirements, the rolling bearing used at a sheet sending part of the office machinery has been more reduced in size, faster working conditions and trended to be higher load.
Especially, the rolling bearing used to heat rolls at a toner fixing part or pressure rolls is worked at high temperatures as 200 to 250xc2x0 C., since a step of using the rolling bearing heats to fuse a toner on a sheet to fix thereon, and the working conditions are more severer (parts other than the toner fixing part are at 100 to 150xc2x0 C.).
The rolling bearing used to heat rolls at the toner fixing part or the pressure rolls has been demanded to be lower in a consumed energy when the rolling bearing is rotated, that is, to be low torque of the rolling bearing for saving the energy.
Besides, as recycling use of units of the heat roll parts has been advanced for curtailing resources, the rolling bearing used therefor is requested to be a longer life under circumstances at high temperatures.
In addition, it has been required for the heat roll to have characteristic less to escape heat at high temperature outside therefrom for saving the energy.
At first, explanation will be made to problems of the prior art rolling bearing used in the vicinity of the heat source as transporting systems within furnaces at high temperatures or the iron-steel equipment.
The inner rings, outer rings and rolling elements of the rolling bearings as above are often composed with a steel for bearing (SUJ2) having high heat conductivity as 50 W/mxc2x7K. Therefore, in case the rolling bearing is disposed nearly to the heat source, the heat therefrom is easy to conduct to the interior of the rolling bearing, and in particular, either near to the heat source of the inner ring and the outer ring, that is, saying in the above example, the temperature of the outer ring faster goes up.
Accordingly, there were risks that a lubricant existing on the raceway surface of the outer ring (for example, silicone grease or fluorine based grease) was oxidized and worsened in a short time, separated an oil content or dissolved, so that the lubricity of the lubricant was deteriorated to extremely shorten the life of the rolling bearing.
Next reference will be made to problems involved with the conventional rolling bearing for fan motors.
Recently, accompanied with miniaturization of electric or electrical machinery, the miniaturization has been progressed also as to fans for internal cooling or blowing air. Particularly, as microprocessors to be incorporated in personal computers, servers or the like also increase heating values together with heightening of calculation processing speed, the cooling fans to be used in this technical field have been demanded, together with the miniaturization, to increase an air quantity and to lower the air blowing temperature.
An air blowing capacity of the fan is determined by the size and rotation number of the fan, and for increasing the air blowing capacity while miniaturizing the size, it is necessary to increase the rotor rotation number of the motor.
In air blowers of air conditioners, the fan has been advanced to have a high output for realizing rapidly cooling or warming. For these fan motors, AC motors by the inverter control are employed, but for making the high output, a carrier frequency from an inverter electric source should be made high frequency.
However, if the electric energy to be supplied to the stator is increased by making the high speed rotation (heightening the rotation number) and the high output of the fan motor, the heat value becomes large, which is generated in the coil or core forming the magnetic field of the stator. Then, if, like the conventional rolling bearing, the composing members of the rolling bearing for supporting a main shaft of the fan motor are fabricated with such materials having high heat conductivity as bearing steels, the heat occurring in the stator is easily transmitted to the rotor to heighten the temperature of the fan. So, although the air quality is increased, the air blowing temperature goes up, so that the increase of the fan cooling effect is probably hindered.
Since the temperature of the rolling bearing itself also goes up, the viscosity of the lubricant charged in the rolling bearing goes down to cause bad lubricity, and therefore if a bearing ring and rolling elements are both composed with a metal, there appear problems of adhesion or fine seizure to bring about a deterioration in the acoustics in the bearing in an early period of service.
Problems with the conventional rolling bearings for office machinery will be explained.
The reduction in size, high speed of serving conditions, high load or high temperature of the conventional rolling bearings make it difficult to form an oil film of the lubricant at the contacting face between the rolling elements, movable member and supporter of the rolling bearing, and trend to lower the lubrication.
Therefore, under such severe conditions, the lubricity is insufficient in the conventional rolling bearing, and by the use for a relatively short time, the torque of the rolling bearing is remarkably increased and is probable to generate seizure owing to abrasion. Thus, in the rolling bearing used to the office machinery of high performance and reduction in size, there is a first problem that the conventional rolling bearing is not suited.
With respect to the rolling bearing used to the heat rolls at the toner fixing part or the pressure rolls, because of the usage under high temperature for the reasons stated in the paragraph of the prior art technique, the request for being at the low torque for saving the energy, and the request for having the long service life under the high temperature aiming at the recycle use saving the resources, the application of the conventional rolling bearing is more difficult (a second problem).
In the rolling bearing used to heat rolls at the toner fixing part or the pressure rolls, it is often use the fluorine grease having the base oil of kinematic viscosity being relatively large at normal temperature (40xc2x0 C.), taking heat resistance and lubricity at high temperature into consideration. However, there is a problem that since the fluorine grease has the high viscosity, the torque becomes large when rotating the rolling bearing, and the energy (electric power) is consumed.
In addition, as stated in the paragraph of the prior art, the heat roll has been required to have characteristic less to escape heat at high temperature outside therefrom for saving the energy. However, as the rolling elements, movable member and supporter of the conventional rolling bearing are composed of metallic materials having the excellent heat conductivity, there arises a third problem that the heat heightened for fixing the toner escapes outside from the heat roll through the rolling bearing used to the heat roll, and the energy (electric power) for heating is more consumed.
Thus, the invention has a first theme of solving the problem involved with the prior art rolling bearing to be used in the vicinity of the heat source, and of making the heat from the heat source difficult to conduct the interior of the rolling bearing, aiming at providing the rolling bearing of a long serving life.
The invention has a second theme of solving the problem involved with the prior art rolling bearing for fan motors, and of having no probability of hindering increase of the cooling effect of the fan in spite of high speed rotation and high output of fan motors, aiming at providing the rolling bearing for fan motors having excellent quietness for a long period of service.
The invention has a third theme of solving the above mentioned third problem among the problem points of the rolling bearing for the office machinery, and decreasing heat radiation from the heat roll, aiming at providing the rolling bearing enabling to make the office machinery save the energy.
For solving the above first theme, the invention has the following structure. The rolling apparatus according to the invention, which is provided with a movable member enabling rotation or linear motion, a supporter for supporting the movable member, and a plurality of rolling elements disposed between the movable member and the supporter for rolling together with the rotation or the linear motion of the movable member, and located in the vicinity of a heat source, is characterized in that at least the rolling elements, or either of the movable elements and the supporter which either is nearer to the heat source, or either of the movable elements and the supporter which either is nearer to the heat source and the rolling elements are fabricated with a material of a heat conductivity being 40 W/mxc2x7K or less.
Being such a structure, the heat conduction of the heat source from either of the movable elements and the supporter which either is nearer to the heat source is effectively controlled, that is, the heightening of the temperature per unit time is effectively controlled. As a result, the lubricant charged within the rolling apparatus (a later mentioned grease) or the lubricant treated on the surface of the interior (such as a solid lubricant film) can be effectively prevented from deterioration owing to the high temperature (oxidation, decomposition, or oil separation).
Accordingly, a long life can be maintained even under the using condition where the heat source is present outside of (in the vicinity of) the rolling apparatus, and the heat is transmitted through the housing or the shaft to increase the temperature of the rolling apparatus.
For providing the effects as mentioned above, it is necessary that at least the rolling elements, or either of the movable elements and the supporter which either is nearer to the heat source, or either of the movable elements and the supporter which either is nearer to the heat source and the rolling elements are fabricated with the material of the heat conductivity being 40 W/mxc2x7K or less, provided that, for exhibiting the above effects more sufficiently, the heat conductivity is preferably 35 W/mxc2x7K or less, more preferably 30 W/mxc2x7K or less.
If the rolling elements are fabricated with a material of the heat conductivity being 40 W/mxc2x7K or less, more preferably 35 W/mxc2x7K or less, still more preferably 30 W/mxc2x7K or less together with either of the movable elements and the supporter which either is nearer to the heat source, the above mentioned effect may be exhibited more satisfactorily.
With respect to materials for fabricating either of the movable elements and the supporter which either is nearer to the heat source or the rolling members, as far as satisfying the condition of the heat conductivity, no limitation is especially provided.
For example, stainless steels as SUS440 or some sorts of ceramic materials may be listed up, and as the ceramic materials, there are exemplified silicone nitride (Si3N4), zirconia (Zr2), alumina (Al2O3), boron carbide (B4C), boron nitride (BN), titanium carbide (TiC), titanium nitride (TiN), or ceramic based materials where two or more sorts of these substances are compounded.
The ceramic materials for the invention improve fracture toughness or mechanical strength, and therefore may be mixed with fibrous filling materials. Fibrous filling materials are not especially limited in sort, and whisker of silicone nitride or alumina whisker may be taken up as examples.
The invention is available to not only the rolling bearing, but also the rolling apparatus such as linear guide apparatus, ball screws, or linear motion bearings. In case the rolling apparatus is a linear guide apparatus, a slider corresponds to the movable member, and a guide rail corresponds to the supporter. In case the rolling apparatus is a ball screw, a nut corresponds to the movable member, and a screw shaft does to the supporter. In addition, in case the rolling apparatus is a linear motion bearing, an outer cylinder does to the movable member, and a shaft to the supporter.
For solving the above second theme, the invention has the following structure. The rolling bearing according to the invention, which is provided with the rotatably movable member, the supporter for supporting the movable member, and the plurality of rolling elements disposed between the movable member and the supporter for rolling together with the rotation of the movable member, is characterized in that the rolling elements are fabricated with a material of a heat conductivity being 40 W/mxc2x7K or less.
The rolling bearing may be of course sufficient with a rolling bearing charged with the lubricant.
Being such a structure, a heat insulation can be made between the movable member and the supporter, and therefore if the rolling bearing is used as a rolling bearing for the fan motor, in case the fan motor is of the high speed rotation and the high output, the heat generated at the stator can be effectively prevented from transmission to the rotor. Consequently, the temperature of the air blowing of the fan is avoided from rising, and heightening of the cooling effect is not hindered.
Further, as the temperature of the rolling bearing itself is also checked to heighten, it is difficult to cause bad lubricity, so that the rolling bearing has the excellent quietness for a long period of service.
For providing the effects as mentioned above, it is necessary that the rolling elements are fabricated with the material of the heat conductivity being 40 W/mxc2x7K or less, preferably 35 W/mxc2x7K or less for exhibiting the above effects more sufficiently, and more preferably 6 W/mxc2x7K or less.
A lower limit of the heat conductivity is not especially defined, but being too low, a temperature gradient is large between the movable member and the supporter, so that a gap within the bearing is changed to probably decrease rotation precision. Otherwise, since the heat is accumulated at the interior of the fan motor to increase the temperature of the rolling bearing, the life of the rolling bearing might be remarkably lowered. In view of these circumstances, the heat conductivity of the rolling elements is preferably 3 W/mxc2x7K or more.
Accordingly, the heat conductivity of the rolling elements should be 40 W/mxc2x7K or less, preferably 35 W/mxc2x7K or less, more preferably 3 to 35 W/mxc2x7K or less, and still more preferably 3 to 6 W/mxc2x7K or less.
In case, in addition to the rolling elements, at least one of the movable member and the supporter is composed with the material having the heat conductivity being 40 W/mxc2x7K or less, preferably 35 W/mxc2x7K or less, the heat conductivity to the rotor can be checked more effectively, and the above mentioned effects can be enough displayed.
As suitably usable materials, the above stainless steels or the ceramic materials may be exemplified. Sintered alloys or cermet of low heat conductivity may be suitably employed if a flexural strength is 600 MPa or more, preferably 900 MPa or more.
In particular, a partially stabilized zirconia where tetragonal system is mixed in cubic system is preferable as the heat conductivity is low as 3 to 6 W/mxc2x7K. Further in particular, zirconia which is pulverized so that crystal diameter of zirconia phase of cubic system to be matrix is 1.0 xcexcm or less, is more preferable because of being excellent in strength and thermal stability.
The alumina zirconia based material where zirconia and alumina are compounded for improving strength and thermal characteristic is desirable, if crystal grain is adjusted to be 1.0 xcexcm or less, because of the low heat conductivity and the excellent strength.
These sintered substances are preferable if being pressure-sintered, but if the flexural strength is 600 MPa or more, those sintered under atmospheric pressure will be usable.
In the rolling bearing, if designing the radius of curvature in the raceway surface of at least the supporter of the movable member and the supporter to be 52% or more of the diameter of the rolling element, the contacting area between the rolling element and the raceway surface is reduced, so that preferably the heat generated at the supporter is difficult to transmit to the movable member. For making the heat more difficult to transmit, the radius of curvature of the raceway surface is made 53% or more of the diameter of the rolling element.
If the radius of curvature of the raceway surface is too large, the surface pressure between the rolling member and the raceway surface is large correspondingly, so that a durable life of the rolling bearing is probable to shorten. Accordingly the upper limit of the radius of curvature in the raceway surface should be preferably 60% of the diameter of the rolling element.
In case the thickness of the outer ring of the rolling bearing is made larger than the thickness of the inner ring and the diameter in the central position (diameter of a pitch circle) of the rolling element between the outer and inner rings is made small, the moment to be taken for rotating the rolling bearing may be reduced.
For solving the above third theme, the invention has the following structure. The rolling bearing according to the invention, which is furnished with the rotatably movable member, the supporter for supporting the movable member, the plurality of rolling elements disposed between the movable member and the supporter for rolling together with the rotation of the movable member, and the lubricant charged in the space provided with the rolling elements therein between the movable member and the supporter, is characterized in that at least the rolling elements are fabricated with a material of a heat conductivity being 40 W/mxc2x7K or less.
With respect to the rolling bearing of the invention, in the rolling elements, movable member and supporter, since rolling surface or the whole of at least the rolling elements is composed with the material having the heat conductivity being 40 W/mxc2x7K or less, when the rolling bearing is used to the heat roll, it is possible to prevent the heat from escaping outside through the rolling bearing from the heat roll at high temperature, and cause to save the energy in the office machinery. Hereafter, a property difficult to escape the heat will be called as anti-heat radiation.
In case the heat conductivity exceeds 40 W/mxc2x7K, the heat escaping outside via the rolling bearing from the heat roll is extremely much, and accordingly the electric power necessary for heating the heat roll is so much and the energy is considerably consumed.
For fully displaying the above effects, preferably the heat conductivity of the material composing at least the rolling elements is 35 W/mxc2x7K or less.
As the desirably used materials of the heat conductivity being 40 W/mxc2x7K or less, the above mentioned ceramic and glass are listed up, and actually enumerated are silicone nitride (Si3N4), sialon, partially stabilized zirconia (ZrO2), ceramic as alumina (Al2O3), or glasses as soda-lime glass and borosilicate glass. These ceramic and glass may be singly used or mixed together with two kinds or more.
When the rolling surface or the whole of at least the rolling element are composed with the ceramic or the glass, even if the contacting face between the rolling elements, movable member and supporter of the rolling bearing is not fully formed with the lubricant film, the rolling bearing can be worked for a long period and the torque life is long under severe conditions of high speed, high load, high temperature and the like, since the ceramic or glass have the low surface energy and the excellent heat resistance and are less to adhere.
In case the movable member and the supporter are formed with a metal material as SUJ2, if the rolling surface or the whole of the rolling element is composed with material having the heat conductivity satisfying the following conditions, the purposes of the invention can be accomplished.
The rolling bearing according to the invention, which is provided with the rotatably movable member, the supporter for supporting the movable member, the plurality of rolling elements disposed between the movable member and the supporter for rolling together with the rotation of the movable member, the lubricant charged in the space furnished with the rolling elements therein between the movable member and the supporter, and the movable member and the supporter being composed with a metal material, is characterized in that a ratio of k1/k2 of the heat conductivity k1 of the material composing the rolling element and the heat conductivity k2 of the material composing the movable member and the supporter is 0.80 or less (hereafter called as xe2x80x9cthe rolling bearing A for the office machineryxe2x80x9d). The temperature of the rolling bearing used in the office machinery, in particular at the heat roll of the toner fixing part is around 200xc2x0 C., and the above mentioned heat conductivity k1, k2 ranges 0 to 300xc2x0 C.
Being such a rolling bearing, when the rolling bearing is used to the heat roll, it is possible to prevent the heat from escaping outside through the rolling bearing from the heat roll at high temperature, and cause to save the energy in the office machinery.
If the ratio of k1/k2 of the heat conductivity exceeds 0.80, the heat escaping outside via the rolling bearing from the heat roll is extremely much, and accordingly the electric power necessary for heating the heat roll is so much and the energy is considerably consumed.
For making the anti-heat radiation of the rolling bearing more sufficient, the ratio of k1/k2 of the heat conductivity is preferably set to be 0.70 or less, more preferably 0.65 or less.
The under mentioned rolling bearing can solve the first and second problems of the rolling bearing for the office machinery mentioned in the paragraph of the theme that the invention is to solve.
The rolling bearing which is provided with the rotatably movable member, the supporter for supporting the movable member, the plurality of rolling elements disposed between the movable member and the supporter for rolling together with the rotation of the movable member, and the lubricant charged in the space furnished with the rolling elements therein between the movable member and the supporter, is characterized in that a grease composition containing a thickening agent is the lubricant, said thickening agent being composed of at least one kind selected from layer-like mineral powder, ultra fine particle, and powder of layer-like substance having cleavage, composing elements of which layer-like substance are substantially all non-metallic, (hereafter called as xe2x80x9cthe rolling bearing B for the office machineryxe2x80x9d).
Herein, the grease composition is meant by the base oil, thickening agent and a semi-solid lubricant composed of said thickening agent. As the base oil or the thickening agent, ordinarily used base oil or thickening agent may be used without problems. As the base oil, for example, a silicone oil, or a mineral oil are listed up. As the thickening agent, for example, a solid fluorinated polymer powder, polyurea, metallic soap, silica gel are listed up.
In such a rolling bearing, the grease composition containing the thickening agent is the lubricant, and for reasons as later mentioned in detail, in the compact office machinery of high performance, if the rolling bearing itself is reduced in size and used under the conditions of high speed and high load, the lubricity is not be insufficient. Accordingly, neither the torque of the rolling bearing is remarkably increased by abrasion for a relatively short time, nor the rolling bearing is baked, and the torque life is long.
In particular, if the rolling bearing is used under an atmospheric air, at high temperature and high load, the lubricity is not be insufficient at the heat roll of the toner fixing part or the pressure roll. Accordingly, neither the torque of the rolling bearing is remarkably increased by abrasion for a relatively short time, nor the rolling bearing is baked, and the torque life is long. The rolling bearing is very suited to the recycling use of the heat roll part.
The thickening agent may be, as needed, used singly or in combination of two kinds or more of the above mentioned substances.
The mixing ratio of the thickening agent in the grease composition comprising the base oil and the thickening agent is preferably 0.5 to 15 wt %, more preferably 0.8 to 12 wt %, and most preferably 1 to 10 wt %. If the mixing ratio of the thickening agent is less than 0.5 wt %, an increasing effect of the lubricity is low, and an effect of suppressing leakage or splash of the lubricant cannot be sometime obtained. Further, if being more than 15 wt %, since the ratio of the base oil is decreased, and the kinematic viscosity of the grease composition is exceedingly high, the sufficient lubricity is not available and an abnormal abrasion occurs in a relatively short time and the torque is increased.
When the load is supported by the movable member, the raceway surface of the supporter and the rolling surfaces of the rolling elements, the thickening agent functions to avoid the metallic contact therebetween, and for fully displaying this function, the mixing ratio of the thickening agent is more preferably 0.8 wt % or more. In view of exactly avoiding such occasions that the thickening agent goes into more than necessarily between the raceway surface and the rolling surface to make the torque unstable, or the grease is hardened to heat, the mixing ratio of the thickening agent is desirably 12 wt % or less.
If the mixing ratio of the thickening agent is specified to be the most preferable value of 1 to 10 wt %, the effect mentioned in the above more preferable case is more fully displayed, and the hindering factor is exactly prevented.
If such a rolling bearing is applied to the rolling bearing of the invention or the rolling bearing of the ratio k1/k2 of the heat conductivity being 0.80 or less (the rolling bearing A for the office machinery), it is possible to provide the rolling bearing having the excellent characteristic as mentioned above in addition to the curtailment of the energy of the office machinery by reducing the heat radiation from the heat roll.
As the layer-like mineral powder, mica based minerals, vermiculite based minerals, or montmorillonite based minerals are listed up. The chemical composition of the mica based minerals is expressed with a general expression, XMg2Li (Y4O10) Z2 or XMg2.5(Y4O10) Z2, and the chemical composition of the vermiculite based minerals is expressed with the general expression, X2/3Mg7/3Li2/3(Y4O10) Z2. The chemical composition of the montmorillonite based minerals is expressed with the general expression, X1/3Mg8/3Li1/3(Y4O10) Z2. Herein, in the above general expressions, X is K, Na or Li, and Y is Si or Ge, and Z is F or OH.
It is preferable that the layer-like mineral powder contains, as an inter-layer ion, at least one of lithium ion and sodium ion. If the layer-like mineral powder containing the inter-layer ion having small ion radius is mixed with solvents such as water or oil, it swells by taking in the solvent in crystal layers. Since the grease composition to be used to the rolling bearing of the invention is adjusted by mixing the layer-like mineral powder having the swelling property and the base oil, and a part of the base oil is taken in into the layer-like mineral powder. Accordingly, if the lubricity is short at the contacting face between the rolling elements, the movable member and the supporter of the rolling bearing as mentioned in the above paragraph of the theme that the invention is to solve, the base oil can be supplied to said contacting face. If the base oil exists exceedingly in the contacting face, the excessive base oil can be taken in into the layer-like mineral powder. Thus, the base oil existing in the contacting face can be always maintained at a proper amount, and a good lubricity is available to extend the torque life of the rolling bearing and to effectively avoid the base oil from scattering when working the rolling bearing.
Further, it is more preferable to carry out a hydrophobic treatment on the interface of the layer-like mineral powder with a surface active agent for making hydrophobic. If making the interface hydrophobic, the water is prevented from taking in into the layer-like mineral powder, and the base oil can be taken in selectively and effectively. Therefore, the good lubricity can be maintained for a long period of service to heighten the torque life of the rolling bearing and decrease a dust amount (leakage of the lubricant).
If the surface active agent for making hydrophobic to be used to the hydrophobic treatment contains alkyl group having carbon atoms of eight or more, no limitation is defined, and often used is alkyl amine based surface active agent having functional group such as ammonium chloride, amino group (xe2x80x94NH2 group), hydroxyl group (xe2x80x94OH group) and carboxyl group (xe2x80x94COOH group).
Preferably, the layer-like mineral powder has average diameter ranging 0.05 to 20 xcexcm. If the average diameter is less than 0.05 xcexcm, when mixing with the base oil for adjusting the lubricant, grains of the layer-like mineral powder aggregate one another to generate secondary grains and probably decrease dispersion. If being more than 20 xcexcm, the layer-like mineral powder is difficult to invade between rolling and sliding contact surfaces of the rolling elements, movable member and supporter (hereafter called as xe2x80x9crolling-sliding contact surfacexe2x80x9d), so that the torque of the rolling bearing is largely increased, and as cases may be, the rolling bearing is impossible to operate.
As the ultra particles, there are ultra particle comprising inorganic substance (hereafter called as xe2x80x9cinorganic ultra particlesxe2x80x9d) and ultra particle comprising organic substance (hereafter called as xe2x80x9corganic ultra particlesxe2x80x9d).
The inorganic ultra particle has very small diameter, and a particle shape is almost globular having no corner, and average diameter is preferably 0.1 xcexcm or less. If being more than 0.1 xcexcm, the inorganic ultra particle is difficult to go into between the rolling-sliding contact surface or is probable to bite therebetween. In addition, since a grinding action is caused by the inorganic ultra particle, the raceway surface or the rolling elements of the rolling bearing increase surface roughness in a relatively short time, or abnormal abrasion is often generated, so that the torque of the rolling bearing is largely increased, and as cases may be, the rolling bearing is impossible to operate.
As examples of the inorganic ultra particle, there are enumerated diamond ultra particle (CD), diamond ultra particle whose surface is composed of graphite, fluorene (C60), silicone oxide (SiO2), titanium oxide (TiO2), zirconium oxide (ZrO2), or magnesium oxide (MgO).
Among the inorganic ultra particles, in particular, the diamond ultra particle is very stable chemically and has superior characteristic of very hard and less to be destroyed.
In fluorene C60, units of a benzene ring structure comprising carbon of predetermined number are combined continuously in globe, and fluorene C60 is a globular carbon cluster having carbon number of 60 where the carbon skeleton has a closed shell structure as a soccer ball. Fluorene C60 has the globular molecular structure and has lubricity in itself, and it is known that the crystal structure thereof is not destroyed until around 1500xc2x0 C. and fluorene C60 is very suited as the thickening agent to be added to the grease composition.
Since the inorganic ultra particle has very fine diameter, and a particle shape is almost globular having no corner, the inorganic ultra particle invades between the rolling-sliding contact surfaces of the rolling bearing and rolls on surfaces of the respective members of the rolling bearing to cause micro bearing effect. Therefore, also in the cases of high load, low speed and thin lubricant film, abrasion or seizure caused by contact or aggregation between the contacting faces are prevented, so that a good lubricating condition can be maintained for a long period of time. Further, owing to the micro bearing effect by rolling of the inorganic ultra particle on the surfaces of the members, frictional resistance is reduced.
In particular, the diamond ultra particle is vary hard and less to be destroyed, and when it goes into between the contacting faces and rolls on the surfaces of the members, it is least to happen that a shape of the particle is made sharp as a whole by destruction of the particle or keen at corners, so that good lubricating conditions can be maintained for a long period of time. In addition, in case the diamond ultra particle is chemically coated with graphite on the surface, as the lubricity at boundary of the particle itself is advanced by the graphite on the surface, so that good lubricating conditions can be maintained for along period of time. Fluorene C60 has the globular molecular structure and has lubricity in itself, and owing to the micro bearing effect and the lubricity of itself, good lubricating conditions can be maintained for a long period of time.
The organic ultra particle is not especially limited but ultra particle polymer produced by a known technique such as emulsion polymerization, multi-stage emulsion polymerization, suspension polymerization or NAD (non-dispersibility). As the ultra particle polymer, there are enumerated, for example, polymer or copolymer of acrylic ester shown with a general expression CH2xe2x95x90CHCOOR as methyl acrylate, ethyl acrylate, acrylate-2-ethylhexyl, and acrylate-n-butyl; polymer or copolymer of ester methacrylate shown with a general expression CH2xe2x95x90C (CH3) COOR as ethyl methacrylate, glycidyl methacrylate, cyclohexyl methacrylate, hydroxtetyl methacrylate, methacrylate n-butyl, hexyl methacrylate, and methyl methacrylate; or styrene polymer, copolymer of styrene-ester acrylate, and copolymer of styrene-ester methacrylate.
The above grease compositions are adjusted by mixing the organic ultra particle and the base oil, and are filled in a space between the movable member and the supporter. Therefore, even if the organic ultra particle exists between the rolling-sliding contact surfaces and the base oil is not sufficient, the members of the rolling bearing are prevented from directly contacting one another.
The organic ultra particle is an intramolecular bridging high molecule having an internal three dimensional network structure, a so-called micro gel, and is very soft in comparison with metals or inorganic substances which are materials for composing the movable member, supporter and rolling elements. Therefore, the organic ultra particle neither damages the members of the rolling bearing nor accelerates abrasion.
The organic ultra particle has the bridging structure, and when mixing with solvents, it is not melted into the solvent but takes in the solvent into the bridging structure, and swells. In the rolling bearing of the invention, since the base oil is mixed with the organic ultra particle having a swelling property, a part of the base oil is taken in into the organic ultra particle. When the base oil lacks in the rolling-sliding contact surface, the base oil taken in the organic ultra particles existing between the rolling-sliding contact surfaces maybe supplied in the lacking rolling-sliding contact surface. When the base oil exists excessively in the rolling-sliding contact surface, it may be taken in among the organic ultra particle existing between the rolling-sliding contact surfaces. Therefore, the base oil existing in the rolling-sliding contact surface can be maintained at a proper amount, and can be effectively avoided from splashing when working the rolling bearing.
The organic ultra particle is ordinarily formed to be globular. In case of being globular, owing to the micro bearing effect by rolling of the organic ultra particle on the surfaces of the members, the frictional resistance is reduced at the rolling-sliding contact surface. Accordingly, fluctuations of the torque and seizure can be effectively prevented, and the good lubricating conditions can be maintained for a longer period of time.
It is preferable that the organic ultra particle is hydrophobic. Being hydrophobic, a water is prevented from entering into the organic ultra particle, and the base oil can be taken in selectively and effectively, so that the good lubricating conditions can be maintained for a longer period of time, and the torque life of the rolling bearing is extended while dust may be decreased. The surface active agent for making hydrophobic to be used to the hydrophobic treatment is the same as the case of the layer-like mineral substance.
The organic ultra particle can be modified on the surface with functional groups such as amino group (xe2x80x94NH2 group), hydroxyl group (xe2x80x94OH group), carboxyl group (xe2x80x94COOH group), and carbonxe2x80x94carbon double bond group of polymerization (Cxe2x95x90C group) Otherwise, it may be modified with a polymer chain which is formed with the carbonxe2x80x94carbon double bond group, and this polymer chain is grafted. By performing such a treatment on the surface of the organic ultra particle, the dispersion to the base oil is stabilized and adsorption to the members is increased, so that the good lubricating conditions can be maintained for a longer period of time.
Preferably, the organic ultra particle has average diameter ranging 0.02 to 1 xcexcm. If the average diameter is less than 0.02 xcexcm, when mixing with the base oil for adjusting the lubricant, the organic ultra particles aggregate one another to generate secondary particles and probably decrease dispersion. If being more than 1 xcexcm, the layer-like mineral powder is difficult to invade between the rolling-sliding contact surfaces, so that the torque of the rolling bearing is largely increased, and as cases may be, the rolling bearing is impossible to operate.
As the powders of the layer-like substances having cleavage where all the composing elements are substantially non-metallic, listed up are amino acid compound (N-lauroyl.L lysine), melamine cyanurate (MCA), carbon fluoride, fluoride pitch, fluoride graphite, or hexagonal boron fluoride (hBN).
Among the powders of the layer-like substances having cleavage where all the composing elements are substantially non-metallic, N-lauroyl.L lysine is expressed with the following chemical formula, having a cleavable lamella structure as graphite.
C11H23CONH(CH2)4CH(NH2)COOH 
Melamine cyanurate (MCA) is ordered in plane in that melamine molecule and cyanuric acid molecule are combined alternately and strongly by hydrogen bond, and the planes are overlapped one another with weak combining force as van der Waals forces, having a cleavable lamella structure as graphite.
Carbon fluoride, fluoride graphite and fluoride pitch are shown with composition formulae of (CF)n, (CF2)n and (C2F)n, and can be easily obtained by fluorinating a carbon source using a fluorinating agent as fluoride gas. The carbon source is not especially limited. Mary kinds of carbon source can be used, for example, crystalline graphite, pitch, amorphous carbon and so on. In addition, not completely fluorinated substances, that is, unreacted carbon remaining substances may be employed.
The above mentioned amino acid compound (N-lauroyl.L lysine), melamine cyanurate (MCA), carbon fluoride, fluoride graphite, and fluoride pitch have the cleavable layer-like crystal structure such as graphite or hexagonal boron fluoride, physically adsorb to the rolling-sliding contact surface and cleave, and therefore even if the lubricity by the base oil between the rolling-sliding contact surfaces is insufficient, the rolling-sliding contact surfaces are prevented from directly contacting one another, and the frictional coefficient is decreased. Therefore, abrasion is difficult to occur at the rolling-sliding contact surface, and increase of the torque and seizure can be effectively prevented.
By the way, it is preferable that the powders of the layer-like substances having cleavage where all the composing elements are substantially non-metallic have average diameter ranging 0.05 to 20 xcexcm. If the average diameter is less than 0.05 xcexcm, when mixing with the base oil for adjusting the lubricant, particles of the layer-like powder aggregate one another to generate secondary particles and probably decrease dispersion. If being more than 20 xcexcm, the layer-like powder is difficult to invade between the rolling-sliding contact surfaces, so that the torque of the rolling bearing is largely increased, and as cases may be, the rolling bearing is impossible to operate.
As above mentioned, depending on kinds of the thickening agents, desirable average diameters are different. The reasons therefor will be explained by example of the layer-like mineral powder and inorganic ultra particles.
The particle of the layer-like mineral powder has a fish scale-like shape, and thickness smaller than that of the average diameter. The layer-like mineral powder is easy to cleave and soft, and if the average diameter preferably ranges 0.1 to 10 xcexcm, the layer-like mineral powder may go into between the rolling-sliding contact surfaces and does not injure the rolling-sliding contact surface. However, if the shape is globular as the inorganic ultra particle, the grains having the average diameters exceeding 0.1 xcexcm (particles larger than thickness of the oil film intervening between the rolling-sliding contact surfaces) sometimes do not go into between rolling-sliding contact surfaces, and since the inorganic ultra particle is hard, the particles having the average diameter exceeding 0.1 xcexcm is probable to cause abrasion in the rolling-sliding contact surface. Thus, the layer-like mineral powder and the inorganic ultra particle are different in ranges of preferable diameters.
The grease composition may be mixed, as needed, with additives in ranges so far as not spoiling purposes. As additives to us used, antioxidant, corrosion prevention or extreme pressure agent will be enumerated.
The rolling bearing as mentioned under may solve the first and second problems of the rolling bearing for the office machinery mentioned in the paragraphs referring to the themes that the invention is to solve, and in particular the rolling bearing is low in torque and may contribute to the saving of the energy of the office machinery such as copiers, laser beam printers, facsimile, or their compound machinery.
The rolling bearing according to the invention, which is provided with the rotatably movable member, the supporter for supporting the movable member, the plurality of rolling elements disposed between the movable member and the supporter for rolling together with the rotation of the movable member, the lubricant charged in the space furnished with the rolling elements therein between the movable member and the supporter, is characterized in that the lubricant has the grease composition where the base oil and the thickening agent composed of solid fluorinated polymer are main components and an oil separation for 24 hours at 200xc2x0 C. or lower is 16.0% or less, said base oil being composed of liquid fluorinated polymer and having kinematic viscosity of 200 to 700 mm2/sec at 40xc2x0 C. (hereafter called as xe2x80x9cthe rolling bearing C for the office machineryxe2x80x9d).
It is preferable that the amount of charging the grease composition in the space is 8 to 23 vol % of a capacity of the space (the inside space capacity of the bearing).
Preferably, the grease composition has the solid lubricant of 0.5 to 5.0 wt %, said solid lubricant being composed of at least one kind selected from layer-like mineral powder, ultra fine granulate, and powder of layer-like substance having cleavage, composing elements of which layer-like substance are substantially all non-metallic.
In the compact office machinery of high performance, if the rolling bearing itself is reduced in size and used under the conditions of high speed and high load, the lubricity is not be insufficient. Accordingly, neither the torque of the rolling bearing is remarkably increased by abrasion for a relatively short time, nor the rolling bearing is baked, and the torque life is long.
In particular, if the rolling bearing is used under an atmospheric air, at high temperature and high load, the lubricity is not be insufficient at the heat roll of the toner fixing part or the pressure roll. Accordingly, neither the torque of the rolling bearing is remarkably increased by abrasion for a relatively short time, nor the rolling bearing is baked, and the torque life is long. The rolling bearing is very suited to the recycling use of the heat roll part.
As the grease composition as mentioned above is filled as the lubricant, the rolling bearing is low torque and much contributes to the curtailment of the energy.
Accordingly, if such a rolling bearing is applied to the rolling bearing of the invention or the rolling bearing (the rolling bearing A for the office machinery) where the ratio k1/k2 of the heat conductivity is 0.80 or less, it is possible to provide the rolling bearing having the excellent characteristics as said above in addition to the curtailment of the energy of the office machinery by decreasing the heat radiation from the heat roll.
It is preferable that the kinematic viscosity of the base oil of the grease composition at 40xc2x0 C. is 200 to 700 mm2/sec as mentioned above. If the kinematic viscosity is less than 200 mm2/sec, when the temperature becomes near 200xc2x0 C., the base oil easily gets out of the rolling bearing in company with the rotation of the rolling bearing, lacks in an amount of working as the lubricant, and insufficient in forming the oil film at the contacting point between the rolling elements and the inner-outer rings. As a result, since the rolling elements and the inner-outer rings directly contact (metal-metal contact), the life of the rolling bearing is sometimes extremely shortened.
If the kinematic viscosity is more than 700 mm2/sec, a stirring resistance of the grease composition is very large, and the torque of the rolling bearing becomes large and consumption of the electric power is large, accordingly.
In short, if the kinematic viscosity of the base oil of the grease composition at 40xc2x0 C. is 200 to 700 mm2/sec, the base oil does not get out outside when the rolling bearing is rotated, so that the lubricant film is fully formed and the stirring resistance is low, and the torque of the rolling bearing is small and the consumption of the electric power may be lowered with the long life of the rolling bearing.
The kinematic viscosity of the base oil of the grease composition at 40xc2x0 C. is preferably 250 to 650 mm2/sec, more preferably 300 to 600 mm2/sec.
The above grease composition is preferably 16.0% or less in the oil separation at 200xc2x0 C. or lower for 24 hours. If being more than 16.0%, the base oil is easy to leak outside of the rolling bearing, and is short in an amount of working as the lubricant, and insufficient in forming the oil film at the contacting point between the rolling elements and the inner-outer rings. As a result, since the rolling elements and the inner-outer rings directly contact (metal-metal contact), the life of the rolling bearing is some times extremely shortened, and at the same time the base oil leaking outside will stain sheets (for example, copy papers) to be used in the office machinery.
For the oil separation of the grease composition to be 16.0% or less, the amount of the thickening agent (the solid fluorinated polymer) contained in the grease composition should be 15 wt % or more.
That is, if the oil separation is not more than 16%, when using the grease composition, the base oil is difficult to get out of the rolling bearing, so that the oil film contributing to the lubrication is sufficiently formed, and the rolling bearing with a long life may be obtained.
The oil separation at 200xc2x0 C. or lower for 24 hours is preferably 15.5% or less, more preferably 15.0% or less. It is possible thereby to steadily prevent the leakage of the base oil in the grease composition and to make the above effects secure.
It is preferable that the amount of charging the grease composition in the space is 8 to 23 vol % of a capacity of the space. If being less than 8 vol %, the amount of the lubricant is insufficient, the rolling bearing becomes seized in a short period. If exceeding 23 vol %, the stirring resistance of the grease composition is considerably large, so that the rotation torque of the rolling bearing is large, and accordingly the consumption of the electric power is large.
In short, when the charging amount is 8 to 23 vol %, the lubricant is fully secured with the long life, the small torque of the rolling bearing and the low consumption of electric power.
The amount of charging the grease composition in the space is more preferably 10 to 21 vol % of a capacity of the space, still more preferably 10 to 18 vol %. In such a way, the above mentioned effects can be provided more steadily.
Further, it is preferable for the grease composition to contain the solid lubricant 0.5 to 5.0 wt %. If being less than 0.5 wt %, an effect heightening the lubricity cannot be sometimes obtained. Exceeding 5.0 wt %, the grease composition becomes extremely hard, and consequently the torque of the bearing is very large, so that the consumed electric power is large.
When containing the solid lubricant 0.5 to 5.0 wt %, the lubricity of the rolling bearing is heightened with the long life, and as the grease composition is not hard, the rotation torque of the rolling bearing is small and the consumed electric power may be reduced.
The amount of solid lubricant in the grease composition is more preferably 0.8 to 4.0 vol %, still more preferably 1.0 to 3.0 vol %. In such a way, the above mentioned effects can be provided more remarkably.
For the solid lubricant, it is sufficient to use singly one kind or combine two kinds or more of the layer-like mineral powder, ultra fine particle, and powder of layer-like substance having cleavage, composing elements of which layer-like substance are substantially all non-metallic. Incidentally, this solid lubricant is also served as the thickening agent.
Preferable embodiments as the solid lubricant are as follows.
(1) The interface of the solid lubricant is performed through the hydrophobic treatment with the surface active agent for making hydrophobic (treated to expel the water and selectively inlet or outlet the oil).
(2) The layer-like mineral powder is at least one kind selected from the group comprising mica based minerals, vermiculite based minerals, or montmorillonite based minerals.
(3) The layer-like mineral powder contains, as an inter-layer ion, at least one of lithium ion and sodium ion.
(4) The ultra particle is at least one kind selected from diamond ultra particle (CD), diamond ultra particle whose surface is composed of graphite, fluorene (C60), silicone oxide (SiO2), titanium oxide (TiO2), zirconium oxide (ZrO2), or magnesium oxide (MgO).
(5) The average diameter of the ultra particle is 0.1 xcexcm or less.
(6) The powders of the layer-like substances having cleavage where all the composing elements are substantially non-metallic, are at least one kind of amino acid compound (N-lauroyl.L lysine), melamine cyanurate (MCA), carbon fluoride, fluoride pitch, fluoride graphite, or hexagonal boron fluoride (hBN).
(7) The average diameters of the layer-like mineral powder or the powders of the layer-like substances having cleavage where all the composing elements are substantially non-metallic, are within the range of 0.05 to 10 xcexcm.
Detailed explanation of the solid lubricant is the same as in the thickening agent of the rolling bearing B for the office machinery, and it is omitted.
The rolling apparatus of the invention is especially suited when used nearly to the heat source, or applied to the fan motor or the office machinery, and of course it can display the excellent characteristics when applied to any other machinery or to usage.
Of the rolling apparatus according to the invention, the rolling bearing can be served to various rolling bearings, for example, a deep groove ball bearing, angular ball bearing, cylindrical roller bearing, needle roller bearing, thrust ball bearing, thrust cylindrical roller bearing, or the like.